In a conventional solid polymer electrolyte fuel cell (hereinafter, referred to as “PEFC”), electric energy generated by an electrochemical reaction produced in a membrane electrode assembly (hereinafter, referred to as “MEA”) that comprising a plate electrolyte membrane and electrodes (a cathode and an anode) arranged on both sides of the electrolyte membrane, respectively is extracted to an outside of the PEFC via separators arranged on both sides of the MEA. This PEFC can be actuated in a low temperature region and is generally used at an operation temperature of about 80° C. to 100° C. Furthermore, because of high energy conversion efficiency of 30% to 40%, short start-up time, and small-sized and lightweight system, the PEFC is expected as an optimum power source of a battery car or a portable power supply.
Meanwhile, a unit cell of a conventional PEFC comprises such constituent elements as an electrolyte membrane, a cathode and an anode each comprising a catalyst layer, and a separator, and its theoretical electromotive force is 1.23 volts. Such a low electromotive force is insufficient as a power source of the battery car or the like. Due to this, a stack fuel cell configured by arranging end plates or the like on both ends of a laminated body, in which unit cells are laminated in series in a lamination direction, is normally used as a power source. It is, however, preferable to downsize a unit cell and to increase an electric-power generating reaction area (output density) per unit area so as to further improve electric power generation efficiency of the PEFC (hereinafter, sometimes simply referred to as “fuel cell”).
In order to increase the output density of the conventional plate fuel cell (hereinafter, sometimes referred to as “plate FC”) per unit area and to improve the electric power generation efficiency thereof, it is necessary to thin the above constituent elements of the plate FC. However, if thicknesses of the constituent elements of the plate FC are set to be equal to or smaller than predetermined thicknesses, functions, strengths and the like of the respective constituent elements may possibly be lowered. For this reason, it is structurally difficult to increase the output density of the fuel cell configured as stated above per unit area to be equal to or higher than a certain density.
From these viewpoints, studies about a tubular fuel cell (hereinafter, sometimes referred to as “tubular FC”) have been recently conducted. A unit cell of the tubular FC comprises a hollow-shaped MEA (hereinafter, simply referred to as “hollow MEA”) that comprises a hollow electrolyte layer and hollow electrode layers arranged inside and outside of the hollow electrolyte layer, respectively. An electrochemical reaction is produced by supplying reaction gases (a hydrogen-based gas and an oxygen-based gas) to the inside and outside of the hollow MEA, respectively, and electric energy generated by the electrochemical reaction is extracted to the outside via current collectors arranged inside and outside of the hollow MEA. Namely, the tubular FC facilitates extracting the electric energy by supplying one of the reaction gases (the hydrogen-based gas or oxygen-based gas) to the inside of the hollow MEA comprised in each tubular FC cell and the other reaction gas (the oxygen-based gas or hydrogen-based gas) to the outside of the hollow MEA. As can be seen, by supplying the same reaction gas to outside surfaces of two adjacent tubular FC cells in the tubular FC, it is possible to dispense with separators that have gas shielding performance in the conventional plate FC. Accordingly, the tubular FC efficiently enables downsizing of the unit cells.
On the other hand, to further improve the power generation performance of the tubular FC, it is preferable to improve efficiency (current correction efficiency) for extracting the electric energy generated in each of the tubular FC cells to the outside. Such improvement in the current collection efficiency can be attained by such means as one for contacting a current collector with a plurality of tubular FC cells.
Several techniques intended to improve the current collection efficiency of the tubular FC have been disclosed so far. For example, Japanese Patent Application Laid-Open (JP-A) No. 2004-288542 discloses a technique relating to a fuel cell system that comprises a cell assembly formed by connecting a plurality of tubular FC cells to one another via cell-connection conductor members and an electrode-connection conductor member electrically connected to the cell assembly. With the technique disclosed therein, the connection between the cell-connection conductor members and the electrode-connection conductor member each comprising a current collecting capability is maintained, so that a fuel cell having a stable electric power generation performance can be provided. Furthermore, JP-A No. 8-162142 discloses a technique relating to a solid PEFC comprising a plurality of tubular FC cells and a baffle. With the technique disclosed therein, a solid PEFC having an improved electric power generation performance can be provided.
However, the technique disclosed in JP-A No. 2004-288542 has the following problem. Since the cell assembly can be connected to the electrode-connection conductor member via the cell-connection conductor members and the respective tubular FC cells, connection resistance is possibly increased and current collection efficiency is possibly deteriorated. Further, the technique disclosed in JP-A No. 8-162142 has the problem that the current collection efficiency is difficult to improve.
It is, therefore, an object of the present invention to provide a fuel cell module comprising a tubular fuel cell and capable of improving current collection efficiency and a fuel cell comprising the fuel cell module.